Antique Induction / Spark Gap/ Ruhmkorff Coil With Rule Measure

This is a quite rare British Antique Induction / Spark Gap / Ruhmkorff Coil With Rule Measure, possibly made for the GPO.  A great find for all collectors of vintage technology and early radio / telegraphy aficionados.

The top of the wood base has the following labels and a a white bakelite rule labelled 0-50 which, I think ..., measures the spark length which is linearly proportional to the voltage:

• B (Battery): The terminal that connects to the positive side of the DC power source or battery, providing the initial voltage.
• P (Primary): The terminal connected to the primary coil circuit. On classic induction coils, this connects to the interrupter (vibrator) which rapidly opens and closes the circuit.
• S (Secondary): The terminal connected to the very fine wire of the secondary winding, which outputs the final high-voltage spark. 

Approximate Size:

• Width: 15.2 cm (6")
• Height: 5 cm
• Depth: 8.9cm
  

The wood plinth and components are in fairly good condition with scratches, scuffs, and blemishes commensurate with age and use. It is being sold as a collectible, for display only, and has not been tested.

Induction coil or spark coils were used in early radio signalling testing, (see attached schematic), however the function of this induction coil was possibly not so benign. Shock Therapy was used extensively in Victorian and Edwardian times as a Quack cure, or at least as a therapeutic device, for a multitude of complaints and illnesses. We think this device dates to the Edwardian period: early 20th Century.

This particular device is portable, being quite small. It would have been powered from a battery-not included.

Accessories shown in one of the images are for illustration only and are not included.

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Spark Gap Transmitter and Induction Coils

A spark-gap transmitter is a device that generates radio frequency electromagnetic waves using a spark gap. This was the technology used in the first thirty years of radio transmission (1887- 1920s), using morse code, prior to the introduction of radio valves/ vacuum tubes. In order to create a spark gap you need an induction/ spark coil, (also known as an inductorium or Ruhmkorff coil after the inventor, Heinrich Rumhkorff), which produces high voltage pulses from low voltage DC.

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